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Construction of Buildings in Bushfire-Prone Areas

What is Bushfire Attack Level BAL-Low? It’s a based on insufficient risk to warrant specific bushfire construction requirements predicted on minimal threat vegetation and non-vegetated areas. This will improve the construction of buildings and home from the elements from the bushfire attack.

By improving the ability of buildings in bushfire-prone areas to withstand attack from bushfire, there is an increase in the protection afforded to building occupants (until the fire front passes) as well as to the building itself.

BAL CHART

Roof Penetrations BAL 12.5 (Formerly medium – Level 1) and BAL 19 (Formally High – Level 2)

BAL 12.5 it is concerned with the protection of your building from ember attack and heat up to and including 12.5 kW/m² (kilowatt-hours per square meter per day).

BAL 19 The increasing levels of ember attack and burning debris ignited by windborne embers together with increasing heat flux greater than 12.5 kW/m² and equals or less than 19 kW/m²

This will apply to roof penetrations:

  • Roof penetrations, including skylights, roof ventilators, roof-mounted evaporative cooling units, aerials, vent pipes and solar panels, shall be adequately sealed at the roof to prevent gaps greater than 3 mm. The material used to seal the penetration shall be non-combustible.
  • Openings in vented skylights roof ventilators or vent pipes shall be fitted with ember guards made from a mesh or perforated sheet with a maximum aperture of 2 mm, made of corrosion-resistant steel, bronze or aluminium.
  • All glass overhead glazing shall be Grade A laminated safety glass complying with AS 1288.
  • Glazed elements in skylights may be of polymer, provided a Grade A safety glass diffuser, complying with AS 1288, is installed under the glazing. Where glazing is an insulating glazing unit (IGU), Grade A toughened safety glass, minimum 4 mm, shall be used in the outer pane of the IGU.
  • Flashing elements of tubular skylights (eg. Sunpipe tubelight) may be of a fire-retardant material, provided the roof integrity is maintained by an under-flashing of a material having a flammability index no greater than 5.
  • Evaporative cooling units shall be fitted with butterfly closers at or near the ceiling level or, the unit shall be fitted with non-combustible covers with a mesh or perforated sheet with a maximum aperture of 2 mm, made of corrosion-resistant steel, bronze or aluminium.
  • Vent pipes made from PVC are permitted. (Not Permitted in BAL-19)

Roof Penetrations BAL 29 (Formerly Very High – Level 3)

Increasing levels of ember attack and burning debris ignited by windborne embers, together with increasing heat flux greater than 19kW/m² and equals or less than 29 kW/m²

This will apply to roof penetrations:

  • Roof penetrations, including roof lights, roof ventilators, roof-mounted evaporative cooling units, aerials, vent pipes and supports for solar collectors, shall be adequately sealed at the roof to prevent gaps greater than 3 mm. The material used to flash the penetration shall be non-combustible.
  • Openings in vented roof lights, roof ventilators or vent pipes shall be fitted with ember guards made from a mesh or perforated sheet with a maximum aperture of 2 mm, made of corrosion-resistant steel, bronze or aluminium.
  • All overhead glazing shall be Grade A safety glass complying with AS 1288.
  • Glazed elements in roof lights and skylights may be of polymer, provided a Grade A safety glass diffuser, complying with AS 1288, is installed under the glazing. Where glazing is an insulating glazing unit (IGU), Grade A toughened safety glass minimum 4 mm, shall be used in the outer pane of the IGU.
  • Where roof lights are installed in roofs having a pitch of less than 18 degrees to the horizontal, the glazing shall be protected with ember guards made from a mesh or perforated sheet with a maximum aperture of 2 mm, made of corrosion-resistant steel, bronze or aluminium.
  • Evaporative cooling units shall be fitted with butterfly closers at or near the ceiling level, or the unit shall be fitted with non-combustible covers with a mesh or perforated sheet with a maximum aperture of 2 mm, made of corrosion-resistant steel, bronze or aluminium.
  • External single pane glazed elements of roof lights and skylights, where the pitch of the glazed element is 18 degrees or less to the horizontal, shall be protected with ember guards made from a mesh or perforated sheet with a maximum aperture of 2 mm, made of corrosion-resistant steel, bronze or aluminium.

Roof Penetrations BAL 40 (Formerly Severe – Level 4)

Increasing levels of ember attack and burning debris ignited by windborne embers, together with increasing heat flux and with the increased likelihood of exposure to flames greater than 29 kW/m² and equal or less than 40 kW/m²

This will apply to roof penetrations:

  • Roof penetrations, including roof lights, roof ventilators, aerials, vent pipes and supports for solar collectors, shall be adequately sealed at the roof to prevent gaps greater than 3 mm. The material used to flash the penetration shall be non-combustible.
  • Glazed assemblies for roof lights and skylights shall have an FRL of –/30/–.
  • Where roof lights are installed in roofs having a pitch of less than 18 degrees to the horizontal, the glazing shall be protected with ember guards made from a mesh or perforated sheet with a maximum aperture of 2 mm, made of corrosion-resistant steel or bronze.

 

Roof Penetrations BAL - FZ (Formerly Extreme – Level 5)

Direct exposure to flames from fire front in addition to heat flux and ember attack with heat greater than 40kW/m²

  • Roof penetrations, including roof lights, roof ventilators, aerials, vent pipes and supports for solar collectors, shall be sealed with mineral fibre at the roof to prevent gaps. Where the gap between the roof covering and the roof penetration is greater than 3 mm, the material used to seal the penetration shall be non-combustible.
  • Roof lights and roof ventilators shall be one of the following:
    •  A system complying with AS 1530.8.2 when tested from the outside.
    • A system with an FRL of 30/30/30 or −/30/30 when tested from the outside.

 Where your building is greater than 100m from any classified vegetation the BAL rating will more than likely be BAL–LOW and will not require any special construction requirements. Where there is a risk or potential that ember attack could affect your home, we recommend that BAL – 12.5 is applied. You must able to see how your bushfire attack level will be reduced and it can make a huge difference in protecting your home.

It should be borne in mind that the measures contained in this Standard cannot guarantee that a building will survive a bushfire event on every occasion. This is substantially due to the degree of vegetation management, the unpredictable nature and behaviour of fire, and extreme weather conditions (AS 3959–2009).

 

Construction of Buildings in Bushfire-Prone Areas